The present invention relates to the formation and utilization of silane-modified inorganic polymeric materials which impart non-Newtonian pseudoplastic properties to aqueous systems. More particularly, the present invention relates to the formation of a water-based drilling fluid containing the subject material and to methods of using such fluids in the drilling of subterranean soils.
In normal well drilling operations in which a well is drilled by a rotary method, the well bore hole is generally filled with a drilling fluid or mud which is circulated therein. Drilling fluids are usually pumped down through the drill stem of the rotary rig, circulated around the drill bit and returned to the surface through the annular passage between the drill stem and well casing. These drilling fluids perform a number of functions including lubricating the drill stem and bit, cooling the bit, carrying the cuttings from the bit up the bore hole to the surface where the cuttings may be separated and disposed of, and providing a hydrostatic head against the walls of the well to prevent the collapse of the walls of the bore hole.
A primary requisite of a satisfactory drilling fluid is its ability to readily circulate and flow, that is, have low viscosity, under the high shear conditions which are present in the environs of the drill bit while, at the same time, being capable of having and maintaining sufficient viscosity to be capable of efficiently carrying the bit cuttings to the surface. It is highly desired that a drilling fluid be capable of exhibiting low viscosities under high shear conditions while also being capable of exhibiting comparatively high viscosities and carrying power under varying low shear conditions which are exerted in the annular passage between the drill stem and the well casing during the fluid's upward movement. In generic terms, a drilling fluid must exhibit non-Newtonian properties as a pseudoplastic fluid, especially under varying low shear rates.
The drilling fluid must also be capable of exhibiting the above-described pseudoplastic properties under changing environmental conditions encountered during a drilling operation due to the bore hole traversing various strata such as shales, clay, etc., and the cuttings of these materials becoming dispersed in the fluid media. The filling fluid components should be substantially stable to the presence of various calcium compounds and to sodium chloride which may be present in the fluid from the soil strata in which it is in contact and/or due to the use of salt water having calcium or sodium salts therein to form the drilling fluid.
It is also well known that as the bore hole increases in depth the temperatures encountered substantially increase above that found at the earth's surface. This is especially a problem found in drilling at depths greater than about 9,000 feet as is presently becoming a more common practice. Further, heat is also generated by frictional forces on the drill bit. It is, therefore, preferred that components used in drilling fluids be stable with respect to varying elevated temperatures.
The drilling fluid must be capable of lifting and removing the cuttings out of the hole on its upward circulation. During this upward circulation, the drilling fluid undergoes varying low shearing rates such as from about 10 to 500 sec.sup.-1 and must have and maintain a substantial viscosity in order to effectively remove the cutting materials. The more rapidly these materials are removed, without the necessity of further grinding and pulverizing to a fine particle size by the drill bit, the more effectively the drill is permitted to act upon new subterranean soil and thereby cause an efficient drilling operation.
A wide variety of drilling fluids have been used, including aqueous based liquids, hydrocarbon based liquids, air and other gases, mist, foams and the like. For most applications the utilization of gases has been found to be impractical, as these materials do not have the density required to counterbalance the subterranean formation pressures which are encountered. Further, the gases do not readily remove the cuttings without their being finely pulverized by the drill bit. The utilization of gases as a drilling fluid thus does not generally permit an efficient deep drilling operation.
Since great volumes of drilling fluids are required for the purposes of providing a cooling medium for the rotary bit and a means of carrying off the drilled particles, the conventional fluids used in this application are based on water. Water alone, being a Newtonian fluid, does not have the needed capability to efficiently carry the drilled particles from the bore hole to the surface. This becomes increasingly apparent as the bore hole increases in depth.
It is widely held and accepted theory that viscosities suitable for creating a particle carrying capacity in the fluid can best be achieved with fluids having non-Newtonian, pseudoplastic properties, that is, that the viscosity must be sufficient to prevent the drilled particles from separating from the drilling fluid when the agitation of the fluid has diminished. For example, a drilling fluid must have a low viscosity under the high shear rate encountered at the drill bit while having the ability to increase in viscosity (and, therefore, particle holding power) under decreasing shear rates encountered in its upward movement.
In order to obtain the desirable viscosity properties, clay or colloidal clay bodies such as bentonite of Fuller's earth have been added to drilling fluids. As a result, such drilling fluids have been usually referred to as "muds". The use of clay-based drilling fluids has provided the means of initially meeting the two basic requirements of drilling fluids, i.e., cooling and particle removal. However, the clay-based drilling fluids are highly unstable when they come in contact with various salts found in drilled earth formations.
Materials which have come into expanding use as components of drilling compositions are Xanthan gums such as are described in U.S. Pat. Nos. 3,198,268; 3,208,526; 3,251,147; 3,243,000; 3,307,016 and 3,319,715. These materials have been found to cause aqueous solutions, such as drilling fluids, to exhibit pseudoplastic properties under varying low shear forces. However, these materials, whether used alone or in combination with other additives, present the problem of being irreversibly degraded by the elevated temperatures encountered during conventional drilling operations and thereby require continuous supplementation of material. The high cost of the Xanthan gums, and the high rate of degradation, limits their usefulness to specialized operations.
There is a general need for a drilling fluid which is capable of being produced at low cost and which renders an aqueous drilling fluid pseudoplastic so as to permit ease of fluidity under high shear conditions such as found at the drill bit site, while being capable of acting as an efficient carrier and remover of drilled particles.